1. Field of the Invention
The present invention relates to a method of protecting a hard disk drive (HDD) from shocks, and more particularly, to a method of protecting a head and a disk in a HDD from shocks and an apparatus therefor by detecting the movement of the HDD using the amount of jitter in servo signals and unloading the head if the movement of the HDD is great enough to damage the head and the disk.
2. Description of Related Art
Hard disk drives (HDDs) are devices that read and write information on a disk. In general, information is recorded on concentric tracks on a surface of at least one magnetic recording disk. The disk is rotatably mounted on a spindle motor, and read/write means, that is, a read/write head, is mounted on an actuator arm that is rotated by a voice coil motor (VCM) accesses the information. The VCM is excited by current to rotate an actuator and move the read/write head. The read/write head senses variations of a magnetic field on the surface of the disk and reads the information recorded on the surface of the disk. Current is supplied to the read/write head so that the read/write head can write information on the data tracks. The current generates a magnetic field and the magnetic field magnetizes the surface of the disk.
HDDs are sensitive to external shocks and vibrations. External shocks or vibrations applied to HDDs may apply physical impacts to a head, resulting in a collision between the head and a disk. Therefore, such shocks and vibrations should be prevented.
As HDDs are persistently miniaturized, they can now be applied to many mobile systems, such as notebook computers, MP3 players, cellular phones, personal digital assistants (PDAs), and so on.
However, HDDs applied to mobile systems are generally subject to more and greater external shocks than those applied to fixed systems like desktop computers. Thus, HDDs should have sufficient shock resistance.
To solve the problem, methods have been suggested for sensing external shocks to compensate themselves or to stop some operations of disk drives until the external shocks are removed. Such methods mainly use a vibration accelerometer or a shock sensor mounted on the disk drives.
Apparatuses for sensing external shocks to perform counter-operations in HDDs are disclosed in Japanese Patent Laid-Open Publication Nos. 2001-266466 (published on Sep. 28, 2001), 1999-39785 (published on Feb. 12, 1999), 2001-014783 (published on Jan. 19, 2001), 1994-302090 (published on Oct. 28, 1994), 1993-101520 (published on Apr. 23, 1993), 1994-309824 (published on Nov. 4, 1994), for example.
However those apparatuses for protecting heads using shock sensors are available only when external shocks are directly applied to HDDs, that is, only when the shock sensors can detect the external shocks. HDDs used in mobile systems may be damaged not only by physical and direct shocks but also by violent movement or falling.
Accordingly, it may be more effective to predict external shocks great enough to damage a head and a disk before the shocks are actually applied and take measures to protect the head and the disk.
The shock resistance of HDDs is approximately 200 to 300 G when a head is loaded on a disk, while that of HDDs is 1000 G or more when the head is unloaded from the disk. Here, G is a unit to indicate one kilogram (1 Kg) with an acceleration of gravity (9.8 m/s2) being applied.
Accordingly, it is easily known that higher shock resistance could be obtained if the head is unloaded in predicting external shocks before those are actually applied.
FIG. 1 is a plan view of a conventional HDD.
A HDD 100 includes at least one disk 112 that is rotated by a spindle motor 114. The HDD 100 also includes a head 120 located adjacent to a surface of the disk 112.
The head 120 can read or record information from or on the disk 112 by sensing a magnetic field formed on the surface of the disk 112 or magnetizing the surface of the disk 112. Although one head is shown in FIG. 1, it should be appreciated that the head 120 consists of a write head for magnetizing the disk 112 and a read head for sensing the magnetic field of the disk 112.
An air bearing is generated between the head 120 and the surface of the disk 112. The head 120 is coupled to a head-stack assembly 122. The head-stack assembly 122 is attached to an actuator arm 124 having a voice coil 126. The voice coil 126 is located adjacent to a magnetic assembly 128 that supports a VCM 130. Current supplied to the voice coil 126 creates a torque that tends to rotate the actuator arm 124 relative to a bearing assembly 132. The rotation of the actuator arm 124 causes the head 120 to traverse the surface of the disk 112.
Information is stored in circular tracks of the disk 112. In general, the disk 112 includes a data zone on which user data is recorded, a parking zone on which the head 120 is parked when the HDD 100 is not used, and a maintenance cylinder. The kind of the head 120, correction values of recording parameters at high and low temperatures, and correction values of the recording parameters according to the kind of the head are stored in the maintenance cylinder.
FIG. 2 is a block diagram of a control system 200 for controlling the HDD 100 shown in FIG. 1.
Referring to FIGS. 1 and 2, the control system 200 includes a controller 202 coupled to the head 120 via a read/write (R/W) channel circuit 204 and a read pre-amp/write driver circuit 206. The controller 202 may be a digital signal processor (DSP), a microprocessor, or a microcontroller.
The controller 202 supplies a control signal to the R/W channel circuit 204 to read data from the disk 112 or record data on the disk 112.
Information is typically transmitted from the R/W channel circuit 204 to a host interface circuit 210. The host interface circuit 210 contains a control circuit for interfacing with a system, such as a personal computer (PC).
In a read mode, the R/W channel circuit 204 modulates an analog signal, which is read by the head 120 and amplified by the read pre-amp/write driver circuit 206, into a digital signal so as to be read by a host computer (not shown), and outputs the digital signal to the host interface circuit 210. In a write mode, the host interface circuit 210 receives user data from the host computer, converts the user data into current so as to be recorded on the disk 112, and outputs the current to the read pre-amp/write driver circuit 206 through signal processing.
The controller 202 is also coupled to a VCM driving circuit 208 that supplies driving current to the VCM 126. The controller 202 supplies a control signal to the VCM driving circuit 208 to control the excitement of the VCM 130 and the movement of the head 120.
The controller 202 is coupled to a read-only memory (ROM) 214 or a non-volatile random access memory (RAM) 216, such as a flash memory. The memories 214 and 216 contain commands and data used by the controller 202 to execute software routines.
The software routines include a seek routine that moves the head 120 to one track to another track, and a following routine that searches for a target sector in the track. The seek routine includes a servo control routine necessary for guaranteeing the head 120 to be moved to a correct track.
The controller 202 takes shock-absorbing measures according to the detection result of the shock sensor 212.
FIG. 3 is a diagram of the shock sensor 212 shown in FIG. 2.
As shown in FIG. 3, the shock sensor 212 includes a piezoelectric sensor 12 for sensing physical shocks and a converter for converting the result obtained by the piezoelectric sensor 12 into an electrical signal. The shock sensor 12 is attached in the HDD, particularly, to a printed circuit board (PCB) in the HDD.
However, since the conventional HDD as shown in FIG. 2 detects physical and direct external shocks using the shock sensor, it can be effectively used only when the shocks are actually applied to the HDD.